There is a considerable, growing demand for microelectronic, opto-electronic, photovoltaic, bio-systems, optics systems, and micro-electromechanical systems on insulator substrates and on durable, and even light weight and flexible substrates such as metal, ceramic, glass, and plastic foils. There is also a demand for such systems on extremely large substrates such as in display applications. Fabricating high performance systems on these substrates is very challenging since these substrates can have intolerable surface roughness and often display thermal and mechanical instability during the fabrication processes flow. In addition, in situations where these systems are desired on large substrates, the lithography tools are extremely expensive or non existent. Furthermore, the fabrication of high quality opto-electronic, bio-systems, photovoltaic, optics systems, and micro-electromechanical, systems directly on non-conventional substrates can suffer from the limitation imposed by maximum process temperature tolerated by the substrates themselves. With these constraints it is virtually impossible to achieve system performances equivalent to that seen, for example, on conventional substrates such as silicon wafers.
Attempting to address this problem researchers have employed mother substrates and separation layers to build devices and systems followed by separation from the mother substrate and application to a permanent substrate. A number of groups have developed separation approaches but these are limited in their applicability.
Shimoda and Inoue (T. Shimoda, S. Inoue, “Surface free technology laser annealing (SUFTLA),” International Electron Device Meeting (IEDM) Tech. Dig., 2289-2292 (1999)) have used a-Si:H as a sacrificial (release) layer with a physical separation approach. This method cannot be used in process flows where temperatures above 400° C. are utilized (due to hydrogen out-diffusion from a-Si:H). This method also requires a transparent mother substrate to allow laser beam impingment.
T. J. Rinke et al. (T. J. Rinke, R. B. Bergmann, and J. H. Werner, Quasi-monocrystalline Silicon for Thin Film Devices, Appl. Phys. A 68 pp. 705-707 (1999)) have another separation scheme. That scheme uses electrochemically etched silicon as the separation layer but which can only use silicon as the mother substrate and this mother substrate is partially consumed in the electro-chemical etch step needed to create the separation layer.
There has also been considerable work done by a number of groups using silicon wafers as the mother substrate for the so-called SOI technology. These approaches have the names SIMOX, Bonding/thinning, or Smart-cut, depending on the specifics of the approach. All start with the size and material limitations of single crystal Si wafers (e.g., see MRS Bulletin, Material Research Society, Volume 23, Number 12, December 1998).
Asano and Kinoshita have also demonstrated a separation approach resulting in TFTs on a plastic substrate. However, this approach is based on using glass as the mother substrate and then etching (dissolving) the glass away to achieve release. Because of its use of low temperature glass, the process is limited in the temperature range allowed for processing and, of course, their mother substrate is not reusable.
Other separation techniques involving the mechanical separation of separation layer are described in U.S. Pat. Nos., 5,811,348; 6,486,041; 6,214,701; 6,225,192; 6,159,824; 5,854,123 and in DE 198 41 430 A1, EP 00993 029 A3, and EP 0 797 258. Separation by exfoliation of a separation layer is described in U.S. Pat. No. 6,372,608.
Even with this work on separation layers there remains a need in the art to fabricate systems and devices that can readily be used on non-conventional substrates. This invention uniquely answers that need of fabricating high performance systems for non-conventional substrates by fabricating the desired system in a building layer or layers on a “mother” substrate using a stabilized sacrificial layer, releasing the fabricated system from the mother substrate, and simultaneously controlling any stress associated with this fabrication/release procedure. The invention enables large area, high quality systems to be fabricated on high-temperature tolerant mother substrates such as fused silica, quartz, or silicon sheets and then to be transferred to non-conventional, even temperature-intolerant substrates. The transferred system can be further encapsulated to improve robustness, mechanical stress resistance, and environmental stability. In the case where the final positioning is on a flexible substrate, the systems of the final structure can be located at or near the neutral bending plane thereby minimizing the mechanical stress during any bending or flexing of the final substrate. In the case of very large final substrates all lithography issues can be circumvented by the use of tiling. In another variant of the invention, the final substrate may be placed on the system before separation thereby eliminating any defined transfer step to the final substrate.